Have you tried e-bay? On the Lucasarts Website, classic games PC page, X-Wing Alliance is still listed. If you contact them, they might be able to hook you up, who knows. They are in the business to make money and if they still have one sitting around collection dust why wouldn't they want to get rid of it and sell it. Also, ocaisonally I see those things at used game stores.
Go big or go home.